<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let num=+prompt("请输入年份：")
        if(num%4===0 && num%100!==0 || num%400===0){
            alert("这一年是闰年")
        }else{
            alert("这一年是平年")
        }
    </script>
</body>
</html>